Optical isolators have been used in the front end of optical systems and other optical components to allow forward light to pass with a low insertion loss and to prevent the light reflected from various external components from interfering with the optimal operation of the various components used in the optical system. This reduces the frequency instability of the laser source, reduces power intensity fluctuations of the optical input signals, and in addition, reduces the overall noise level of the laser and system thereby providing for a higher signal to noise ratio of the system overall. In an optical communication system, a fiber optical isolator allows higher quality optical signals to be transmitted and for passive components to be able to receive these higher quality signals as well.
Recently, high power fiber lasers and fiber amplifiers that are used to amplify optical signals have replaced the solid state laser sources and the gas laser sources that have been widely used in material processing, industrial manufacturing and ultra long distance communication. With these new higher power components, the prior art optical isolators have been unable to efficiently or effectively handle the high optical power.
In particular, when an optical fiber isolator is operated using higher optical power, e.g., >10W, the prior art isolators exhibited several weaknesses that resulted in the isolators being damaged by the high power optical signals. Another issue with prior art optical isolators is backward light propagation.
Therefore what is needed is an optical isolator that provides for the transmission of high optical power signals in a first direction, but prevents other light from disrupting or interfering with the desired optical signal due to the issues with the prior art described above.